RESUMEN
Application of radio frequency (RF) electromagnetic waves enhances the electrocatalytic water oxidation by protonated tetraruthenium polyoxometalate ([Ru4(µ-O)4(µ-OH)2(H2O)4(γ-SiW10O36)2]10-). In particular, an enhancement factor of 3.6 is achieved when the level of proton substitution of protonated tetraruthenium polyoxometalate is changed from zero to 9 under application of RF at 200 MHz.
RESUMEN
Electromagnetic waves, such as microwaves, have been used to enhance various chemical reactions over polyoxometalates. The dielectric properties of catalysts are among the relevant parameters facilitating catalytic reactions under electromagnetic radiation. This study describes the dielectric properties of polyoxometalate catalysts in aqueous and organic solutions to understand the mechanism of interactions between polyoxometalates and electromagnetic waves. Specific loss factors of polyoxometalates were observed at lower frequencies (<1 GHz) by the ionic conduction of the polyoxometalate solution. The evolution of ionic conduction depended strongly on cations rather than anions. Proton-type polyoxometalates exhibited significantly higher loss factors than other cations did. The activation energy for ionic conduction in protonated silicotungstic acid (H4SiW12O40) was significantly low in water (7.6â»14.1 kJ/mol); therefore, the high loss factor of protonated polyoxometalates in water was attributed to the proton relay mechanism (i.e., Grotthuss mechanism). The results suggested that the proton relay mechanism at the radio-frequency band is critical for generating selective interactions of polyoxometalates with applied electromagnetic fields.